In the past, headstock assemblies have been relatively large components of a chucker and bar machine. Most of the adjunct components have been secured to the machine base rather than the headstock, since the headstock tends to grow significantly in the course of long operation due to heat build up in the headstock. Heat build up causes substantial changes in various areas of the headstock and particularly in the area of the bearings which support the spindle. Because of this, severe stress and loads on the headstock amplify deviations and reduce accuracy. In the past, standard chucker and bar machines had difficulties in maintaining accuracies of between one and three thousandths of an inch. Further, prior developments, would mount the brake mechanism directly on the base rather than on the headstock in order to reduce deflection and distortion of the headstock, so as to increase accuracy during prolonged use.
Additionally, no mechanism was provided for balancing of the spindle itself upon and after installation in the headstock. Thus, in time, spindles due to wear and misalignment would have to be pulled and new spindles repositioned in order to assure continued accuracy.
Other problems with present headstocks include failure to be able to prevent coolant and dirt and dust particles from entering into the headstock assembly. This eventually causes wear and break-downs requiring shutdown of the machine and replacement of parts.
Another problem with present machines is that the touch-off plate is generally mounted in an area which is difficulty accessible on either the headstock or on the base and which requires rather complex gauging devices for accurately determining tool wear as machine operations proceed.
Another problem with present machines is that the headstock mounts have no mechanism for protecting the headstock, should shearing of the bolts holding the headstock to the base occur. Obviously, severe pressures placed on the bolts may cause failure and the whole headstock will tear away from the base causing substantial damage necessitating replacement of substantial components, if not all of the headstock.
In the past, it has been the practice of machine tool manufacturers to mount components such as brake members, collet closers, and spindle encoders directly on the base in order to insure accuracy. This requires increasing the size of the base in order to support all the various components adding to costs.